The invention relates to a heddle shaft having detachable corner connections. More specifically, the invention relates to a heddle shaft wherein the shaft rods include hollow sections into whose hollow space, at each corner connection, a projection extending laterally from the lateral support fits in a plug-like fashion and is clamped by a clamping means.
Heddle shafts usually consist of four basic elements, namely two support rods and two lateral supports connected to the support rods. The point of connection of the support rods with the lateral supports is referred to as a corner connection. In the case of so-called sliderless heddle shafts, when a new warp is to be drawn in, the entire shaft packet is removed from the loom and brought into the drawing-in room. In order to remove the heddles and to draw in new heddles, one of the two lateral supports is usually disconnected. It is obvious that a corner connection wherein the lateral supports can be quickly and easily detached from the shaft rod, and which can be just as quickly reconnected, is advantageous for weaving, because in most cases a lateral support must be removed to draw in new warp threads. In addition, the mounted lateral support must be positioned very precisely in relation to the support rods. If this is not done, disturbances will occur in the weaving operation, causing considerable costs.
Many constructions are in use that meet both requirements. One of the most successful and simplest constructions is disclosed in DE 33 08 371. This construction is based essentially on a projection of the lateral support being braced in the hollow space of the shaft rod by means of a pressure screw. Similar designs operating with the same principle of a pressure screw are found in EP 0 189 216, EP 0 328 953 and DE 40 38 384.
A further construction, though not quite so easy to handle, uses a draw-screw and a wedge which is clamped directly or indirectly in the hollow space of the shaft rod. Such constructions are disclosed in GB 925 562, SU 288 681, JP H3-55865 and CH 404 580. Also proposed have been elements which are movable around a pivot for bracing in the hollow space of the shaft rod, e.g., in EP 0 502 383. JGM H2-132 681 discloses a U-shaped element that is used for clamping a projection of a lateral support, once again by means of a pressure screw.
All of these designs (and there are still more than those listed) have in common that a bracing in the hollow space of the shaft rod occurs which considerably stresses the lateral walls of the shaft rods. Since compared to this prestressing the operating tensions created by the upward and downward motion of the heddle shafts are relatively low, such constructions can be used without a problem up to medium rotational speeds. But the continuously increasing rotational speeds of the loom increase the operating tensions so much that, although no overload breakages occur, fatigue fractures occur fairly quickly. The insertion of elastic parts does not provide a solution, because the level of stress is not reduced by doing so; rather, if anything, it only results in a somewhat reduced fracture frequency. The reinforcement by means of a box-type insert, used in DE 40 38 384, is no longer sufficient at very high rotational speeds either. Only EP 0 189 216 in FIGS. 4 and 5 shows a projection that does not impact the lateral walls of the shaft rod with the initial tension of the clamping screw. On the other hand, the projection of the lateral support that fits into the shaft rod is subjected to strain with these forces. It is also known that it is out of the question to mount a thread with sufficient diameter in the projection of the lateral support for the forces required nowadays. Furthermore, the shaft rod is weakened too much by the slot needed for the screw. Thus, although these are the proper rudiments of a solution to the problem, the proposed design is not realizable in practice.
It is therefore an object of the present invention to create a detachable corner connection for a weaving frame which is able to absorb the bracing and/or prestressing forces which occur during assembling as well as the stresses occurring during operation, and which also allows simple detachment and simple remounting.